1. Field of the Invention
The present invention generally relates to a reflow apparatus for fusing and shaping a solder electrode formed on a semiconductor wafer, and the like; and especially relates to a corrosion prevention technology for a chamber material in a fluxless reflow apparatus wherein a solder electrode is fused and shaped without using flux.
2. Description of the Related Art
A fluxless reflow apparatus is proposed (for example, Patent Reference 1) wherein a solder bump is formed by removing a surface oxide film of a solder electrode using the reduction power of formic acid without using flux in manufacturing a flip chip LSI.
Since flux is not used, according to the fluxless reflow apparatus, a flux washing process that requires an organic solvent for cleaning the solder bump surface after reflow becomes unnecessary, and a manufacturing process can be shortened. Further, by dispensing with the flux washing process currently performed using a great amount of organic solvents, an adverse effect on the environment, especially generating carbon dioxide, can be eliminated.
According to the fluxless reflow apparatus of Patent Reference 1, thermal reflow is performed under reduced pressure. For this reason, almost no gas is taken into the solder bump, and a void is prevented from being produced. Therefore, the reliability of the solder bump is improved.
FIG. 1 shows an outline of a conventional reflow apparatus.
The reflow apparatus has a processing chamber 1 for performing a thermal fusion reflow process, and a formic acid injection mechanism 4.
To the formic acid injection mechanism 4, formic acid in a liquid state is provided through a formic acid introduction pipe 2, and inert gas, such as nitrogen (N2) and argon (Ar), is provided through an inert gas introduction pipe 3.
The introduced formic acid solution and the inert gas are mixed in a spraying nozzle 5, and formic acid atmosphere mist 6a is sprayed from the spraying nozzle 5. The mist state is maintained by an auxiliary heater 7 so that evaporation is promoted, and the sprayed formic acid atmosphere mist 6a is introduced into the processing chamber 1.
In the processing chamber 1 is arranged a semiconductor wafer 9 (wafer) on the surface of which a solder electrode is formed. The wafer 9 is held above a main heater 10 for heating the wafer 9, and is fixed by a wafer fixing mechanism 8. Since the processing chamber 1 is heated by the main heater 10, and is evacuated by an exhausting apparatus (not illustrated), the introduced formic acid atmosphere mist 6a is diffused onto the wafer 9 as formic acid atmosphere gas 6b. 
[Patent reference 1] JPA 2001-244618